Combine fresh pitted cherries, granulated sugar, cornstarch, lemon zest, lemon juice, pure vanilla extract, and Kosher salt in an 11″ tart pan or pie dish, stirring to evenly coat the cherries.
Pour box of chocolate cake mix on top. Spread into an even layer.
Melt unsalted butter, then pour directly on top of cake mix, trying to cover as much of the surface with butter as possible. Do not stir or mix.
Place the cake in a preheated oven and cook until the top is mostly set and the cake has puffed up.
Allow the cake to cool slightly for 5 minutes, then serve immediately. We recommend serving with powdered sugar or fresh whipped cream!